Well that strategy is screwed up if there's hail or sandstorm, switching into an attack, and anything and their mother with a priority move can take it down. I'm not really a fan of revenge killers, so it wouldn't be something I'd use, or be worried about. Besides, the boost would only last one turn either way.
I guess if it only lasted one turn, it wouldn't be that broken, but I don't think Gamefreak will give anything that much of a boost just by switching in. If they do go with an ability that lets you get free boosts when you switch in, they'll go with a +1 boost at first to test the waters.
Lucario generally runs Swords Dance and Extremespeed when not using a Specs set. Lucario doesn't need Agility to pull off a physical sweep, as it has plenty of speed already and a priority move. Heracross has neither. Besides, I doubt Heracross would see any hampering by getting Agility. I mean, most Heracross only need three moves anyway, being Megahorn/Close Combat and a pick of either Stone Edge/Night Slash.
My point being is that instead of focusing on evolutions, perhaps we should take the Heart Gold/Soul Silver route and help improve the existing Pokemon movesets. Not everything needs an evolution/pre-evolution. I mean, look at Mime Jr. for example. Does anyone even use that outside of Little Cup (Or even within Little Cup?)
The point isn't that Lucario has a priority move, it's that Agility Lucario doesn't really work. Lucario only has to run Close Combat, Crunch, and either Stone Edge or HP Ice, if it doesn't have Extremespeed, so Agility can fit right in there. Heracross may have a higher Atk stat, but it still doesn't have enough power to take out something liek Skarmory with only a Guts boost. (A Guts boosted Close Combat from max Atk Heracross only deals 56% - 66.5% to standard Skarmory and won't KO it even with LO and after it switches in on SR.) I agree that we should be focusing on giving the Pokemon new moves before giving them new evolutions, but Agility won't be as useful on Heracross as you think it will.
@ blasphemy1: Not all priority moves are tackling attacks.
Ice Shard: The user flash freezes chunks of ice and hurls them. This move always goes first.
Mach Punch: The user throws a punch at blinding speed. It is certain to strike first.
Shadow Sneak: The user extends its shadow and attacks the foe from behind. This move always goes first.
Ice Shard doesn't even make contact with the opponent. I figure a Bug priority move would work by having the user send a a super fast pulse at the opponent. That would probably be very similar to Sonic Boom, although, I've always thought it should have been a priority move anyway.
I came up some other ideas for moves a while ago, but I forgot about them.
Type: Psychic
Base Power: -
Accuracy: 100
PP: 20?
Priority: 0
Target: Single non-user
Effect: This move exchanges the user type(s) with the opponent. This effect lasts until the Pokemon switches out.
I figure this move will only be used on something that can hit itself SE with its own STAB or 4x with a move. Obviously, the opponent will probably switch out right away. This will probably be used best on a Latias with Draco Meteor or a Celebi with U-turn.
Type: Normal
Base Power: -
Accuracy: -
PP: 20?
Priority: +3 (The same as Follow Me and Protect.)
Target: Self and Ally
Effect: This move swaps the position of the user and the user's ally until the end of the turn. So any move that your opponent chose to hit Pokemon A, would hit Pokemon B instead.
It could be used as an alternative to Follow Me, atleast to prevent Taunt, and could be used with Pokemon that resist each others weaknesses like Jirachi and Salamence to mess with your opponent. I don't think it would have any effect in single battles.